My favourite shops (to note a few) are:
Modcloth -  they are a super cute online store, with a mixture of 50's glam and modern fashion. The shipping was amazingly fast, and you can click on a item you love (that's sold out) to be notified when it's back in stock. There are many reviews on nearly every item, and the customer service is just GREAT!

MaxShop - This is actually the online version of a local shop. I absolutely love going on line looking at the latest styles, then going into the shop the next day to try on the item. Max is a New Zealand brand, which is AWESOME, and has really high quality clothes (although this is reflected in the price).

There are about four sale sites I love:
BuyInvite and NZsale - both these sites manage to source epic sales from epic brands, and allow us (the customer) to purchase products at a fantastic price!
My most recent purchases are some Michael Kors Sunglasses, and a Romeo and Juliet Couture top (more on these when I receive them)
The only down side: It can take a while for items to arrive as they have to wait for the sale to end, then order the item from supplier, and then finally dispatch.

MyHabit - bought to us by Amazon.com is another favourite, and offers again epic brands (this time a bit better known and a bit higher class). Some of my favourite of their sales included; Dolce and Gabbana, Vera Wang and Prada bags.
Of course you have to be in QUICK! and since it's an American site that means me getting up very early.

Reebonz - is a website I have only very recently joined. They again are a sale site, and advertise at selling luxury brands at a discounted price. It is a members only site, and you need to be invited to join. The sales are fantastic! However, the products are a little out of my (student budget) price range.

Finally, Good old ebay and (NZ's version) TradeMe.